1. Technical Field
This invention relates to systems for supplying fuel to the engines of aircraft. Specifically, the invention relates to systems for supplying fuel to aircraft under negative gravity conditions.
2. Background Art
Gravity normally pulls liquid fuel toward the bottom of a tank. For this reason, the fuel systems of surface vehicles such as ships, locomotives and automobiles normally draw fuel from near the lowest point in the fuel tank to fully utilize all available fuel.
Aircraft fuel supply systems present problems not present in surface vehicles. Aircraft may experience negative gravity conditions during high-speed maneuvering and when they fly upside-down. Under negative gravity conditions, liquid fuel moves to the "top" of a fuel cell. If a fuel cell is partially empty, an inlet near what is normally the bottom of the cell loses connection with the fuel. This results in loss of fuel flow to the engines, loss of power and, if the condition continues for sufficient time, engine shutoff. Negative gravity conditions of short duration particularly cause problems when air enters the fuel pump and causes it to lose its prime. Some pumps encounter difficulty resuming flow once fuel is again available at the inlet. Air entrapped in a fuel system can also cause cavitation, vibration and uneven fuel flow to the engine which may result in poor performance ad damage to system components.
Several systems have been previously developed to maintain the supply of fuel to aircraft engines under negative gravity conditions. Examples of such systems are found in U.S. Pat. Nos. 2,660,384, 3,443,778 and 4,203,458. Each of these prior systems draws fuel from what is usually considered the uppermost part of the fuel cell when the aircraft experiences a negative gravity condition. A problem exhibited by these and all other prior systems of which Applicant is aware, is that such systems may pass a large slug of air through the fuel system when they change over from the normal positive gravity condition to a negative gravity condition and vice versa.
A further problem with prior systems is that they add substantially to the weight and cost of an aircraft. For example, there are substantial weight and cost penalties associated with the use of dual impeller pumps such as that utilized in U.S. Pat. No. 2,660,384. The internal baffles in the fuel cells required for operation of the device shown in U.S. Pat. No. 4,203,458 likewise adds weight and cost. Other systems such as those shown in U.S. Pat. No. 3,443,778 employ small valves and flow passages which may become clogged due to dirt in the fuel, and pressure diaphragms which wear and eventually break.
Thus, there exists a need for an apparatus for supplying fuel to an aircraft fuel system under negative gravity conditions which reduces the amount of air that enters the system when the aircraft reverses its gravity condition. Further, there exists a need for an apparatus for supplying fuel to an aircraft fuel system under negative gravity conditions which is lower in weight, less expensive to implement, and more reliable than existing systems.